A major objective for this year will be to determine if any differences exist between cardioselective and noncardioselective beta adrenergic blocking agents on regional myocardial blood flow and contractile function in ischemic myocardium. Equieffective beta 1 receptor blocking doses will be administered in intact dogs. We will study the effects of beta blockade during controlled arterial blood pressure and heart rate to determine the importance of these factors in the beneficial actions of these agents. Pressures, flows and resistances in ischemic myocardium will be measured and calculated to aid in analyses of the mechanism of action of beta blockade on ischemic endo/epi. A second objective for the coming year will be to determine the effect of different types of coronary vasodilators on coronary collateral function during acute myocardial ischemia. Two calcium antagonists, FR 7534 and nifedipine, and nitroglycerin and dipyridamole will be studied. These experiments should help define the primary sites of action of the calcium antagonists in the coronary vascular bed. Experiments will be performed in the presence or absence of drug-induced hypotension. Mechanisms of drug effects on endo/epi will be determined.